Many times, remodeling projects call for altering the wall or wall surface. Whenever walls are to be removed or exposed, do not break into them until you know what is behind them. Walls may hide wiring, plumbing, drain lines and vent pipes, and even heating, air conditioning, and air return ducts in some older homes. Any damage to these could not only be expensive, but disastrous.
Walls can be either load-bearing or non-load-bearing. If you are expanding the bathroom or reconfiguring the walls, be aware of the load-bearing walls in your plan. Load-bearing walls are those that support the weight of the structure above. These make up the frame or skeleton of the house that keeps the structure standing even through wind storms and snow loads. The ends of the ceiling joists must connect to the load-bearing walls for support. If this skeleton is not strong and stable, it will shift and cause the walls to crack, floors to sag, and windows and doors to stick and not move smoothly. Over time it can cause the house to become out of square or plumb.
Removing non-load-bearing walls is usually not a problem when considering structural support of the floors above. Many times, in an effort to open up space, load-bearing walls may need to be removed. As a general rule, you can identify which walls are load-bearing by checking to see in which direction they run. Exterior walls that run perpendicular to the ceiling and floor joists are load-bearing. If you do not have ready access to the joists, you may either need to remove some molding or drill holes in the ceiling to determine where the joists are located.
If load-bearing walls need to be removed, local codes specify the type and length of header that needs to be used to span the opening for support (see Figure 2.3). Usually wood beams will be sufficient for short spans, but steel I-beams or structural beams made of laminated timbers are needed for longer spans.